Bezier Curve TILT or Normal exporting
After quite some research, I am pretty sure it is not possible to directly extract the curve's normals from Blender, but it is possible to extract the control point's TILT values with a Python script. However, I found a solution to recalculate the normals in OpenGL which I will present here in case someone has the same issue in the future. 

I realised that blender calculates the normals using an algorithm which minimises the twisting of the normals compared to the previous values (called "Minimum"). Since I didn't find a way to export these normals from Blender, nor a complete explanation of the algorithm, what I did first was to change the normals' calculation to "Z-UP" in Blender (which is simply another way of calculating normals). Then I imported the curve's control points and handles with a Python script and recalculated the normals in OpenGL as for a standard Bezier curve. Finally, I still had some issues with the twisting and especially where the end meets the beginning of the curve. This problem was solved by calculating the normals using the previous point's normal and adding a low and constant value to the latter's y component.